Add a new interface option 'require_interfaces'

Non-destructive patch, won't affect anything because this
option is not used in any model yet.

Official guide for network.managed state provides an example:
bond0:
  network.managed:
    - type: bond
    - slaves: eth2 eth3
    - require:
      - network: eth2
      - network: eth3
    ...
without parameter: '- use:'

* add a new option 'require_interfaces' that allows to set
  '- require:' not only for 'bridge' interfaces
* using 'require_interfaces' allows to fix the order for states
  that create bonds (do not try to create bond0 before slave
  interfaces are configured!)
* using 'require_interfaces' allows to fix the order for states
  that create VLANs (do not try to create tagged interfaces before
  parent interface is created, it locks the parent interface
  creation!), example: bond0.2516 created before bond0
* using 'require_interfaces' allows to fix the order for states
  that depend on OVS interfaces

Change-Id: Id4539a7e24f2c55fb62afe5d47e485effc9a882b

linux/network/interface.sls

   {%- for param in network.interface_params %}
   {{ set_param(param, interface) }}
   {%- endfor %}
+  {%- if interface.require_interfaces is defined %}
+  - require:
+    {%- for netif in interface.get('require_interfaces', []) %}
+    - network: linux_interface_{{ netif }}
+    {%- endfor %}
+    {%- for network in interface.get('use_ovs_ports', []) %}
+    - cmd: ovs_port_up_{{ network }}
+    {%- endfor %}
+  {%- endif %}
   {%- if interface.type == 'bridge' %}
   - bridge: {{ interface_name }}
   - delay: 0